As a rubber composition used for tire treads of automobiles, there has conventionally been known one in which carbon black is blended as a reinforcing agent together with a rubber component composed of a conjugated diene rubber.
Further, with a recent increasing demand for a reduction in fuel consumption of automobiles, in order to comply with such a demand, for the purpose of a reduction in rolling resistance of tires, silica has been used as a reinforcing agent.
Then, in the rubber composition in which silica is blended as the reinforcing agent, the silica particles are liable to coagulate with each other and less likely to be uniformly dispersed. Accordingly, in order to solve such a problem, various proposals have been made (for example, see Patent Document 1 and Patent Document 2).